Prioritizing vaccine development to focus on pathogens that drive the most antibiotic prescribing will have multiple advantages: reducing the burden of disease, reducing the extent of antibiotic use, and thus reducing the selective pressures driving antimicrobial resistance. In this proposal, we will (1) test the hypothesis that recent declines in outpatient antibiotic prescribing in the US are associated with reductions in pneumococcal disease attributable to PCV13 uptake and (2) estimate the antibiotic prescribing attributable to the most common pathogens and variation by age, demographic, and geography. To do so, we will use large representative nationwide datasets from the US, including insurance claims, public health surveillance, and a national immunization survey. The deliverables from this project will include estimates of the impact of PCV13 on outpatient prescribing and quantification of the expected reductions in antibiotic prescribing given vaccines for common pathogens. We expect that the results from these studies will establish (1) robust estimates of the reductions in outpatient antibiotic prescribing achieved by PCV13, as an exemplar of what vaccines can accomplish; and (2) priorities for vaccines to target in terms of impact on antibiotic prescribing and thus on antimicrobial resistance.